Indicators of Food Microbial Quality and Safety
481
Coliform tests are widely used in shellfish sanitation, but they are not always good predictors of
sanitary quality. The U.S. National Shellfish Sanitation Program was begun in 1925, and the presence
of coliforms was used to assess the sanitation of shellfish-growing waters. Generally, shellfish from
waters that meet the coliform criteria (“open waters”) have a good history of sanitary quality, but some
human pathogens may still exist in these shellfish. In oysters, there is no correlation between fecal
coliforms and Vibrio cholerae
16,41 or between E. coli and either Vibrio parahaemolyticus or Yersinia
enterocolitica.
52 Coliforms are of no value in predicting scombroid poisoning,
52 nor do they always
predict the presence of enteric viruses (see the subsection Coliphages, below). For sanitizing surfaces
in meat packing plants, K. pneumoniae (and possibly Raoultella spp.) might be a better choice than
generic E. coli.
85
In spite of the limitations noted, coliforms are of proven value as safety indicators in at least some
foods. They are best employed as a component of a safety program such as the HACCP system
described in Chapter 21.
Enterococci
Around 30 species of the genus Enterococcus are recognized; and 22 are summarized in Table
20–5. Prior to 1984, the “fecal streptococci” consisted of two species and three subspecies, and they,
along with S. bovis and S. equinus, were placed together because each contained Lancefield group D
antigens. The latter two species are retained in the genus Streptococcus.
Historical Background
Escherich was the first to describe the organism that is now E. faecalis, which he named Micrococcus
ovalis in 1886. E. faecium was recognized first in 1899 and further characterized in 1919 by OrlaJensen.
64 Because of their existence in feces, these classic enterococci were suggested as indicators
of water quality around 1900. Ostrolenk et al.
65 and Burton
9 were the first to compare the classic
enterococci to coliforms as indicators of safety. Pertinent features of the classic enterococci that led
to their use as pollution indicators for water are the following:
1. They generally do not multiply in water, especially if the organic matter content is low.
2. They are generally less numerous in human feces than E. coli, with ratios of fecal coliforms to
enterococci of 4.0 or higher being indicative of contamination by human waste. Thus, the classic
enterococcal tests presumably reflect more closely the numbers of intestinal pathogens than fecal
coliforms.
3. The enterococci die off at a slower rate than coliforms in waters and thus would normally outlive
the pathogens whose presence they are used to indicate.
The simultaneous use of enterococci and coliforms was advocated in the 1950s by Buttiaux,
10 as in
his opinion the presence of both suggested the occurrence of fecal contamination. In his review of the
literature, Buttiaux noted that 100% of human and pig feces samples contained enterococci, whereas
only 86–89% contained coliforms.
10
Classification and Growth Requirements
Although the classic enterococci never achieved the status of coliforms as sanitation indicators for
water or foods, their current classification in an expanded genus could, on one hand, make them more
481
Coliform tests are widely used in shellfish sanitation, but they are not always good predictors of
sanitary quality. The U.S. National Shellfish Sanitation Program was begun in 1925, and the presence
of coliforms was used to assess the sanitation of shellfish-growing waters. Generally, shellfish from
waters that meet the coliform criteria (“open waters”) have a good history of sanitary quality, but some
human pathogens may still exist in these shellfish. In oysters, there is no correlation between fecal
coliforms and Vibrio cholerae
16,41 or between E. coli and either Vibrio parahaemolyticus or Yersinia
enterocolitica.
52 Coliforms are of no value in predicting scombroid poisoning,
52 nor do they always
predict the presence of enteric viruses (see the subsection Coliphages, below). For sanitizing surfaces
in meat packing plants, K. pneumoniae (and possibly Raoultella spp.) might be a better choice than
generic E. coli.
85
In spite of the limitations noted, coliforms are of proven value as safety indicators in at least some
foods. They are best employed as a component of a safety program such as the HACCP system
described in Chapter 21.
Enterococci
Around 30 species of the genus Enterococcus are recognized; and 22 are summarized in Table
20–5. Prior to 1984, the “fecal streptococci” consisted of two species and three subspecies, and they,
along with S. bovis and S. equinus, were placed together because each contained Lancefield group D
antigens. The latter two species are retained in the genus Streptococcus.
Historical Background
Escherich was the first to describe the organism that is now E. faecalis, which he named Micrococcus
ovalis in 1886. E. faecium was recognized first in 1899 and further characterized in 1919 by OrlaJensen.
64 Because of their existence in feces, these classic enterococci were suggested as indicators
of water quality around 1900. Ostrolenk et al.
65 and Burton
9 were the first to compare the classic
enterococci to coliforms as indicators of safety. Pertinent features of the classic enterococci that led
to their use as pollution indicators for water are the following:
1. They generally do not multiply in water, especially if the organic matter content is low.
2. They are generally less numerous in human feces than E. coli, with ratios of fecal coliforms to
enterococci of 4.0 or higher being indicative of contamination by human waste. Thus, the classic
enterococcal tests presumably reflect more closely the numbers of intestinal pathogens than fecal
coliforms.
3. The enterococci die off at a slower rate than coliforms in waters and thus would normally outlive
the pathogens whose presence they are used to indicate.
The simultaneous use of enterococci and coliforms was advocated in the 1950s by Buttiaux,
10 as in
his opinion the presence of both suggested the occurrence of fecal contamination. In his review of the
literature, Buttiaux noted that 100% of human and pig feces samples contained enterococci, whereas
only 86–89% contained coliforms.
10
Classification and Growth Requirements
Although the classic enterococci never achieved the status of coliforms as sanitation indicators for
water or foods, their current classification in an expanded genus could, on one hand, make them more